libstdc++-v3/doc/html/manual/dynamic_memory.html

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   3   Support
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   5 </th><td width="20%" align="right"> <a accesskey="n" href="termination.html">Next</a></td></tr></table><hr /></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="std.support.memory"></a>Dynamic Memory</h2></div></div></div><p>
   6     There are six flavors each of <code class="function">new</code> and
   7     <code class="function">delete</code>, so make certain that you're using the right
   8     ones. Here are quickie descriptions of <code class="function">new</code>:
   9   </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
  10         single object form, throwing a
  11         <code class="classname">bad_alloc</code> on errors; this is what most
  12         people are used to using
  13       </p></li><li class="listitem"><p>
  14         Single object "nothrow" form, returning NULL on errors
  15       </p></li><li class="listitem"><p>
  16         Array <code class="function">new</code>, throwing
  17         <code class="classname">bad_alloc</code> on errors
  18       </p></li><li class="listitem"><p>
  19         Array nothrow <code class="function">new</code>, returning
  20         <code class="constant">NULL</code> on errors
  21       </p></li><li class="listitem"><p>
  22         Placement <code class="function">new</code>, which does nothing (like
  23         it's supposed to)
  24       </p></li><li class="listitem"><p>
  25         Placement array <code class="function">new</code>, which also does
  26         nothing
  27       </p></li></ul></div><p>
  28      They are distinguished by the parameters that you pass to them, like
  29      any other overloaded function.  The six flavors of <code class="function">delete</code>
  30      are distinguished the same way, but none of them are allowed to throw
  31      an exception under any circumstances anyhow.  (They match up for
  32      completeness' sake.)
  33    </p><p>
  34      Remember that it is perfectly okay to call <code class="function">delete</code> on a
  35      NULL pointer!  Nothing happens, by definition.  That is not the
  36      same thing as deleting a pointer twice.
  37    </p><p>
  38      By default, if one of the <span class="quote">“<span class="quote">throwing <code class="function">new</code>s</span>”</span> can't
  39      allocate the memory requested, it tosses an instance of a
  40      <code class="classname">bad_alloc</code> exception (or, technically, some class derived
  41      from it).  You can change this by writing your own function (called a
  42      new-handler) and then registering it with <code class="function">set_new_handler()</code>:
  43    </p><pre class="programlisting">
  44    typedef void (*PFV)(void);
  45
  46    static char*  safety;
  47    static PFV    old_handler;
  48
  49    void my_new_handler ()
  50    {
  51        delete[] safety;
  52        popup_window ("Dude, you are running low on heap memory.  You
  53                       should, like, close some windows, or something.
  54                       The next time you run out, we're gonna burn!");
  55        set_new_handler (old_handler);
  56        return;
  57    }
  58
  59    int main ()
  60    {
  61        safety = new char[500000];
  62        old_handler = set_new_handler (&amp;my_new_handler);
  63        ...
  64    }
  65    </pre><p>
  66      <code class="classname">bad_alloc</code> is derived from the base <code class="classname">exception</code>
  67      class defined in Sect1 19.
  68    </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="support.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="support.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="termination.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 4.
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